A diaphragm valve using a diaphragm as a valve body has been conventionally well known. The conventional diaphragm valve is shown in FIG. 6.
In FIG. 6, a diaphragm valve 1 includes a block-like body 2 having a fluid inflow channel 2a, a fluid outflow channel 2b, and a depression 2c opening upward, a cylindrical hood 3 having a lower end portion screwed into an upper portion of the depression 2c of the body 2 and extending upward, a casing 4 screwed into the hood 3, an annular seat 5 made of synthetic resin and disposed on a circumferential edge of the fluid inflow channel 2a, a diaphragm 6 that is pressed against or separated from the seat 5 to open and close the fluid inflow channel 2a, a diaphragm presser 7 that presses a central portion of the diaphragm 6, and an actuator (not shown) that is built in the hood 3 and the casing 4 and causes the diaphragm 6 to press against and separate from the seat 5 via the diaphragm presser 7.
In such a diaphragm valve 1, improving durability and reliability is an issue to be achieved. For example, in the above-described conventional diaphragm valve 1, as shown in FIG. 7 in an enlarged manner, in the case where a foreign substance A that has got into an area between the seat 5 and the diaphragm 6, there is a fear that leak L might occur.
Patent Literature 1 discloses that, in a diaphragm valve of a type different from that illustrated and described above, providing two projections on a seat achieves double seals, whereby durability and reliability are improved.